It is known to coat non-woven webs with various aqueous based coatings. In many instances it is desired to form a smooth continuous coating such as veneers for simulated wood panelling. Such surfaces must be relatively clear, adhere well to the substrate and be washable. In other applications the product must be soft and flexible such as in coating or impregnating non-woven webs and textiles. Impregnants for foams are also required to be soft and flexible. In all these applications heat sealability can be a requirement.
Polyvinyl chloride is used in some of these applications. Unfortunately, PVC homopolymers are not film forming at low temperatures and tend to be too hard to be useful in these applications. Copolymers of vinyl chloride and "soft" monomers have a reduced hardness but often it is not sufficient for the required application and there may be a sacrifice of other properties. To overcome these problems external plasticizers may be added to the vinyl polymer. This creates a problem for the converter as plasticizer may be lost to the environment during hot operations such as calendering and/or drying. This loss to the atmosphere is becoming more environmentally unacceptable. In some products the plasticizer may migrate to the upper surface resulting in a dirty, greasy appearance, which may be accompanied by "bloom" of chemicals within the PVC coating.
One approach to soften PVC is to blend it with other polymers such as butadiene-acrylonitrile copolymers, acrylate and methacrylate copolymers. Conventional wisdom is that PVC type polymers are incompatible with styrene-butadiene polymers.
The present invention seeks to overcome the above drawbacks by providing a blend of PVC and carboxylated styrene-butadiene type latices, which, surprisingly in view of the incompatibility of the polymers, exhibit extremely useful properties.